This invention relates to a magnetoresistive element and a magnetic recording apparatus, and more particularly to a magnetoresistive element using a spin valve structure, and a magnetic recording apparatus using the magnetoresistive element as its magnetic head.
In general, reading of information recorded on a magnetic recording medium has been conducted by moving a reproducing magnetic head having a coil relative to the recording medium and detecting a voltage induced in the coil by electromagnetic induction generated upon movement of the magnetic head. It is also known to use a magnetoresistive element (hereinafter called xe2x80x9cMR elementxe2x80x9d) for reading out information (see, for example, IEEE MAG-7, 150(1971). Magnetic heads using a MR element (hereinafter called xe2x80x9cMR headxe2x80x9d) relies on the phenomenon that electric resistances of some ferromagnetic materials vary with intensity of external magnetic field.
Along with recent progress toward miniaturization and large capacity of magnetic recording mediums, reproduced magnetic signals of information read out from recording mediums are getting weaker and weaker, and MR heads more sensitive and capable of extracting larger outputs are being anticipated. Especially in multi-layered films having a sandwich structure of ferromagnetic/non-magnetic/ferromagnetic layers, large magnetoresistance effects have been obtained. That is, while applying an exchanging bias to one of two ferromagnetic layers interposing a non-magnetic layer between them so as to pin its magnetization, magnetization of the other ferromagnetic layer is reversed by an external magnetic field (signal magnetic field, for example). Thus, the relative angle of magnetized directions of these two ferromagnetic layers sandwiching the non-magnetic layer is change, and a large magnetoresistance effect is obtained. The multi-layered film of this type is called xe2x80x9cspin valve structurexe2x80x9d (see Phys. Rev. B., Vol. 45, p806 (1992), J. Appl. Phys. Vol. 69, p4774(1991), for example).
Spin valve structures have large magnetoresistance changing rates ranging from 5% to 8% and their magnetization can be changed in low magnetic fields, spin valve structures are suitable for MR elements. However, to cope with higher recording density, larger MR changing rates are needed, and it is desired to increase current MR changing rates to two through three times or more. However, it is difficult to obtain MR changing rates larger than 10% with spin valve structures of a type simply stacking metal layers. Recently, attention has come to be paid to xe2x80x9cspecular spin valve structuresxe2x80x9d made by using an insulating ferroelectric material made of oxides such as NiO, Fe2O3, or the like, as the bias film and stacking an oxide film on the surface of the other magnetic material as well. As to specular spin valve structures, it is known that, by further sandwiching a sandwich film of magnetic/non-magnetic/magnetic layers between insulators, electrons can be specular-reflected at the metal/insulator interface and magnetoresistance effect as large as approximately 20% can be obtained. Specular spin valve structures need sandwiching the magnetic/non-magnetic/magnetic sandwich film with oxide layers from opposite sides thereof, and simultaneously need stacking at least one bias film in contact one of those magnetic layers for pinning magnetization. For this purpose, oxide antiferromagnetic layers of NiO, Fe2O3, or the like, are currently used. Heretofore, however, no satisfactory oxide antiferromagnetic material having an acceptable bias property has been known, and this is a bar against their practical use. That is, not having insulating antiferromagnetic material having a sufficiently large exchange bias magnetic field and a sufficiently high blocking temperature, it is still difficult to use specular spin valve structures as practical materials.
On the other hand, there is a recently proposed method which inserts a very thin oxide in a magnetic layer to obtain specular effect while using a metal antiferromagnetic material. With this method, a large MR effect can be obtained while using a metal antiferromagnetic material having a large exchange bias magnetic field and a sufficiently high blocking temperature. In this case, however, it is important to make the very thin oxide layer with a high accuracy and to make a good oxide layer while ensuring a high reproducibility.
It is therefore an object of the invention to provide a MR element and a magnetic recording apparatus using a MR element which has a pinned layer of a good bias property while using a secular spin valve structure with a large MR changing rate, and is improved in soft magnetic property.
To accomplish the object, a first MR element according to the invention, having a spin valve structure which includes a first magnetic film, a second magnetic film, and a non-magnetic spacer film interposed between the first magnetic film and the second magnetic film, is characterized in that: at least one of the first magnetic film and the second magnetic film includes a first ferromagnetic metal layer; a first non-metal layer provided on the first ferromagnetic metal layer; a second non-metal layer provided on the first non-metal layer and different in composition from the first non-metal layer; and a second ferromagnetic metal layer provided on the second non-metal layer. Thereby, a non-metal layer for specular-reflecting electrons can be made very thin with a good reproducibility.
A second magnetoresistive element according to the invention, having a spin valve structure which includes a first magnetic film, a second magnetic film, and a non-magnetic spacer film interposed between said first magnetic film and said second magnetic film, is characterized in that: at least one of said first magnetic film and said second magnetic film includes a first ferromagnetic metal layer; a second ferromagnetic metal layer provided on said first ferromagnetic metal layer and different in composition from said first ferromagnetic metal layer; a non-metal layer provided on said second ferromagnetic metal layer; and a third ferromagnetic metal layer provided on said non-metal layer. Thereby, a non-metal layer for specular-reflecting electrons can be made very thin with a good reproducibility.
A third magnetoresistive element according to the invention, having a spin valve structure which includes a first magnetic film, a second magnetic film, and a non-magnetic spacer film interposed between said first magnetic film and said second magnetic film, is characterized in that: at least one of said first magnetic film and said second magnetic film includes a first ferromagnetic metal layer; a first non-metal layer provided on said first ferromagnetic metal; a second ferromagnetic metal layer provided on said first non-metal layer; a second non-metal layer provided on said second ferromagnetic metal layer; and a third ferromagnetic metal layer provided on said second non-metal layer. Thereby, a specular-reflection of the electrons can be realized in much improved efficiency.
A fourth magnetoresistive element according to the invention, having a spin valve structure which includes a first magnetic film, a second magnetic film, and a non-magnetic spacer film interposed between said first magnetic film and said second magnetic film, is characterized in that: at least one of said first magnetic film and said second magnetic film includes: a first ferromagnetic metal layer containing at least one element selected from the group consisting of lithium (Li), beryllium (Be), sodium (Na), magnesium (Mg), aluminum (Al), silicon (Si), phosphorus (P), potassium (K), calcium (Ca), scandium (Sc), gallium (Ga), rubidium (Rb), strontium (Sr), yttrium (Y), cesium (Cs), barium (Ba) and elements belonging to the lanthanide series by not less than 1%; a non-metal layer formed on said first ferromagnetic metal layer; and a second ferromagnetic metal layer formed on said non-metal layer. Thereby, a non-metal layer for specular-reflecting electrons can be made very thin with a good reproducibility.
A fifth magnetoresistive element accroding to the invention, having a spin valve structure which includes a first magnetic film, a second magnetic film, and a non-magnetic spacer film interposed between said first magnetic film and said second magnetic film, is characterized in that: at least one of said first magnetic film and said second magnetic film includes a first ferromagnetic metal layer, a non-metal layer provided on said first ferromagnetic metal layer, and a second ferromagnetic metal layer provided on said non-metal layer, said non-metal layer being made of an antiferromagnetic material which satisfies the equation:
Pxc3x97(n+0.3)xe2x89xa6Txe2x89xa6Pxc3x97(n+0.7)
where T is the thickness of said non-metal layer, P is the magnetic period thereof, and n is an integer. Thereby, a high performance MR element can be proposed by realizing a synthetic antiferromagnetic coupling of the magnetic layers.
A sixth magnetoresistive element according to the invention, having a spin valve structure which includes a first magnetic film, a second magnetic film, and a non-magnetic spacer film interposed between said first magnetic film and said second magnetic film, is characterized in that: at least one of said first magnetic film and said second magnetic film includes a first ferromagnetic metal layer, a non-metal layer provided on said first ferromagnetic metal layer, and a second ferromagnetic metal layer provided on said non-metal layer, said non-metal layer being made of an antiferromagnetic material which satisfies the equation:
Pxc3x97(nxe2x88x920.2)xe2x89xa6Txe2x89xa6Pxc3x97(n+0.2)
where T is the thickness of said non-metal layer, P is the magnetic period thereof, and n is an integer. Thereby, a high performance MR element can be proposed by realizing a fairly stable ferromagnetic coupling of the magnetic layers.
The thickness of the non-metal layer is defined as the distance between the centers of the metal atomic layers at the interfaces of the non-metal layer and the neighboring magnetic layers. These metal atomic layers are determined to be the ones adjacent to the oxygen atomic layers at the interfaces and to be outside of the oxygen atomic layers.
In other wards, the thickness of the non-metal layer is defined as the distance between the centers of the metal atomic layers which outwardly abut on the oxygen atomic layers at the interface between the non-metal layer and the neighboring magnetic layers. The definition is applicable to the case where the non-metal layer is made of an oxide compound which has a much more complicated crystal structure.
On the other hand, the magnetic recording apparatus according to the invention includes a magnetic head for recording and reproducing information on or from a magnetic recording medium, which uses any of the above-summarized MR elements, and ensures large reproduction signal outputs and good thermal stability.
The invention is used in the above-summarized modes and brings about the following effects.
First, according to the invention, by interposing a non-metal layer as an electron reflection layer in the pinned layer and stacking two kinds of layers under that non-metal layer, it is possible to fabricate a very thin, even non-metal layer with a good reproducibility by using the lower layer as a stopper layer against reaction. As a result, a good pinning property can be obtained by ensuring magnetic coupling between the first ferromagnetic metal layer and the second ferromagnetic metal layer while having electrons specular-reflected.
Additionally, by making the lower ferromagnetic metal layer of the non-metal layer in the pinned layer in form of a multi-layered structure and using the lower layer as a layer having a high bulk effect and high ferromagnetism, the pinning property is further improved to obtain a large MR changing amount.
Further, according to the invention, by using a multi-layered structure as the ferromagnetic metal layer under the non-metal layer in the pinned layer and using a ferromagnetic layer with a high bulk effect as its underlying layer, the pinning property can be improved more and a higher MR changing amount can be obtained.
Furthermore, according to the invention, by separately providing a plurality of non-metal layers for reflecting electrons in the pinned layer, it is possible to increase interfaces with ferromagnetic layers and thereby increase the probability of electrons being specular-reflected. More specifically, while ensuring magnetic coupling between ferromagnetic layers by using a non-metal layer so thin that pin holes can exist, specular-reflection efficiency of electrons can be increased largely. As a result, while maintaining the pinning property, momentum loss of electrons can be decreased significantly, and a large MR property can be realized.
Moreover, according to the invention, by using a synthetic antiferromagnetic layer as the pinned layer including a non-metal layer in the middle, shifting of the working point caused by the static magnetic field from the pinned layer can be prevented. Further, with no influences from the static magnetic field, the free layer can be made sufficiently thin, and the specular effect can be used more effectively.